How do you change water in larvae tank?

[Spotsmom]

Dumb question but I’ve never kept any aquatic animals. But now I find myself with a tupperware housing some spotted salamander larvae. I understand they need wafter changes, especially after feeding, but how do you keep throwing the larvae out with the water?
The egg mass is also still in the container, but I’m not sure if any more larvae will hatch. I currently see 8-9 that hatched about five days ago.Thanks for your insights!